An effective chemo pre-exposure prophylaxis (PrEP) strategy is predicted to prevent millions of new HIV infections. Intensifying preclinical testing with emphasis on compounds with proven clinical efficacy and combinatorial approaches to increase the breadth of protection and will greatly facilitate in meeting this challenge. While the macaque model has pioneered the anti-HIV PrEP concept and paved the way to the present ongoing clinical trials, a small animal model of HIV infection will speed-up the evaluation of potential PrEP compounds, combinations, doses, and dosing strategies. In this regard, the newly developed humanized mouse models that harbor human HIV target cells show great promise. We and others have recently achieved HIV-1 mucosal transmission via both vaginal and rectal routes in these models and have derived proof-of-concept data so that PrEP strategies can be efficiently tested in this system. A major knowledge gap in the PrEP field is pharmacokinetics and pharmacodynamics (PK/PD) for HIV prevention. Drug efficacy for HIV has usually been defined in small dose finding studies that measure surrogate markers such as plasma viral RNA to define therapeutic effects and establish the correct doses, combinations of doses, and dose frequencies. Surrogate markers of prophylactic effects have not been identified. This has led to the need for large and costly trials having HIV incidence as an outcome to test the efficacy of various HIV chemoprophylaxis regimens. In this regard, the humanized mouse model offers a tremendous advantage in that the dose finding studies can be conducted rapidly with HIV incidence outcomes to define PK/PD and inform rational doses, combinations, and dose frequencies for further PrEP studies. Drawing on expertise from two major labs (Kashuba lab on PK-PD and Akkina lab on humanized mice) a major goal in this proposal is to model PrEP strategies employing HIV itself as the challenge virus and derive important data for further testing in macaques and clinical development. Our specific aims for this three year grant period are to Aim 1. Determine the minimum daily dose of ARVs (CCR5 inhibitor maraviroc, integrase inhibitor raltegravir and RT inhibitors tenofovir and emtricitabine) required to confer complete protection against vaginal HIV-1 challenge. Aim 2. Define PK-PD parameters of the above ARVs by correlating PrEP efficacy with drug concentrations in plasma and vaginal tissues and develop a PK-PD model of drug exposure and prevention in mice. Aim 3. Evaluate combinatorial and intermittent dosing PrEP strategies employing ARVs with different modes of action. PUBLIC HEALTH RELEVANCE (provided by applicant): Chemo-prophylactic drugs that act against HIV and prevent viral transmission are expected to protect millions of at-risk people worldwide. Here we will systematically evaluate four anti-HIV drugs namely, maraviroc, raltegravir, tenofovir and FTC to determine their optimal drug exposure levels needed in plasma and vaginal tissue to confer full protection. These drugs with different modes of action will be tested in a novel humanized mouse model of HIV sexual transmission. In addition to determining their potential efficacy as prophylactics, we will also test their drug distribution in vivo. After determining their efficacy, we will identify the best dosing levels and schedules convenient for widespread use. In addition, we will evaluate if these drugs can be co-formulated with each other in different combinations to design a far superior protective drug regimen with broad spectrum effectiveness even against commonly encountered drug resistant viruses. If successful, these studies will lead to the development of a new potent HIV prevention strategy which is urgently needed to restrain the ongoing AIDS epidemic.